In 1979 Chris Brasher, an Olympic steeplechase champion, travelled to New York to run the city's marathon. It was a trip that left an immediate impression on an athlete who, having been a pacemaker for Sir Roger Bannister when he broke the four-minute mile, was not someone easily impressed.

"Last Sunday," Brasher wrote in the Observer, "in one of the most violent, trouble-stricken cities in the world, 11,532 men, women and children from 40 countries of the world, assisted by 2.5 million black, white and yellow people, Protestants and Catholics, Jews and Muslims, Buddhists and Confucians laughed, cheered and suffered during the greatest folk festival the world has seen."

After lobbying the relevant authorities, Brasher helped to launch the London marathon. When it began in 1981, he had hoped around 4,000 would turn out to race. On the day 7,000 started and most finished. Brasher, then aged 52, completed the race in less than three hours.

The marathon, after several wobbles, has become the capital's biggest single-day festival. For the Virgin London Marathon, about 37,000 people will take part, cheered on by more than half a million spectators. But the event has had a profound influence that stretches far beyond the confines of the M25. Prior to London, distance running had simply been for the athletics elite. London brought running to the masses.

That legacy has mutated over the last 30 years as, buoyed by London's success, running clubs, companies, cities and parks have sought to stage their own long-distance running events, creating an increasingly crowded and eclectic field.

The Runner's World database recorded 145 full marathons in the UK last year, almost three times the 50 held in 2003. The number of half marathons over the same period rose from 189 to 336.

There has also been a huge rise in the number of 10km races, while the success of the free 5km Park Run series has led tens of thousands more people to participate in an organised running event for the first time. In total, the database recorded 3,517 races distance races last year, compared to 2,014 in 2003.

The mainstream events have spawned outliers in the form of ultra marathons (those more than 26.2 miles) and extreme, obstacle-littered races that sell themselves on the sheer levels of pain they can inflict on competitors. Themed races, such as the Rock'n'Roll series, and Nike's Run to the Beat, both set to live music, are hugely popular.

The more astute organisers have turned their races into festivals – mini Glastonburys or Latitudes – that provide facilities and activities not just for competitors but their families.

The popular Loch Ness marathon weekend is more than 10 years old and boasts 9,000 runners (more than 10 times the original number), who compete over 26.2 miles, 10 and five kilometres and, in the case of the under 5s, 400m.

"We are very much a destination event," said Malcolm Sutherland, the race director. "People will come for the weekend and go on and then do something else, like the whisky trail."

Organising the Loch Ness marathon is a full-time job for Sutherland and his team, a sign of how the sport is moving from an amateur era into a more corporate one.

But the plethora of races raises questions about whether the running bubble could burst.

"It's not cheap, putting on a marathon," Sutherland conceded. "Some will find themselves unable to continue."

But such concerns do not deter others from entering a crowded field. Newcomer Xtremerunning.co.uk will stage its first obstacle race, run over either five or 10 kilometres, this June at Gloucester Park in Essex.

"The people who come to us are those who've done a triathlon or have attended boot camps [exercise classes run by military fitness instructors]," said Brian Lee, its co-founder. "They're looking for something more. We get a lot of interest from people talking on Facebook or Twitter."

The increasing popularity of such events, powered in part by social media, may help explain why more people are running.

The government's latest Active People Survey, published last December, revealed that, for the first time, more than 2 million adults now take part in athletics each week. Some have suggested that the economic climate is playing a part. The rising cost of gym membership has led more people to take exercise on trails and roads, rewarding themselves with a race as a training goal.

Others can see an almost spiritual dimension. "As the recession continues to bite into our finances, we are turning to cultural events to affirm our unity rather than our individuality," said Ellis Cashmore, a professor of culture, media and sport at Staffordshire University. "Today's event marathons are secular equivalents of Diwali or Eid al-Fitr."

Whatever the reason, the mass appeal of running has turned hitherto anonymous runners into rock stars. Distance runner Scott Jurek is now feted by sportswear companies, while athletics brands compete to put on high-profile races.

Purists gripe that their sport is being commercialised. But Kym McConnell, the author of Extreme Running, a book that examines 24 races on seven continents, said they were the minority.

"People are just grateful that the races can survive," McConnell said, pointing out that the popular London to Brighton run has returned only recently after being disbanded in 2006.

The trend now is for people to run further, faster, fiercer. The Mont Blanc all-night race had 200 competitors when it started seven years ago. Last year 2,000 competed and 10 times that many tried to enter.

The number of UK ultras recorded by Runner's World rose from 29 in 2003 to 156 last year.

For Bannister, the trend makes perfect sense. "The more restricted our society and work becomes," he once said, "the more necessary it will be to find some outlet for this craving for freedom."